Around 3678 BBY, Darth Marr and several other Dark Councilors confronted the Sith Lord Calypho on the world of Korriban, arresting him for heresy just as Calypho's apprentice Teneb Kel returned from a mission into the planet's ancient tombs. Kel was allowed to participate in the Imperial offensive on Begeren, but after the Invasion of Begeren ended the apprentice was arrested as well. Darth Marr led parades in the streets of Kaas City on the Imperial capital of Dromund Kaas in celebration of the victory, but he afterwards attended a meeting of the Council in their chamber beneath the Imperial Citadel. There, Kel was brought before Darth Marr and the other Dark Councilors and ordered to kill Lord Calypho. Marr noticed that the young Sith drew strength from his fear, causing another Councilor to mock Kel for not drawing upon his anger. When a Councilor halted the battle before Calypho's death, the Sith was taken away by Imperial Guardsmen to be tortured, and Marr reminded the apprentice that he was not special—his master had made him into a disgrace.[9]

However, Marr and several other Councilors recognized that Kel could still be of use as a weapon, and Marr revealed a hologram of the apprentice's target: Exal Kressh, the wayward apprentice of the Sith Emperor. The Dark Councilor brushed aside Kel's questions, informing the young Human that his place in the Empire would be judged again if he succeeded in the mission. He then brought Kel before the Emperor himself, bowing low as the Sith ruler informed Marr's chosen assassin that Kressh could be found in the Lenico system.[9] Kel would eventually successfully track down and kill Kressh on Korriban, though not before learning that the Emperor intended to create his Children—extensions of his will that would spread his influence secretly across the galaxy.[11] During the young Human's report to the Dark Council, he refused to submit to their authority and prompted Darth Marr to summon a storm of Force lightning as a threat. However, Kel convinced the Council to accept his offer: in exchange for information on the Emperor's plans, the Dark Council would grant him the rank of Sith Lord and the title of Darth Thanaton.[12]

Darth Marr was famous to the people of the Empire as their stalwart defender

As the Great Galactic War continued, Darth Marr attained a fearsome reputation among both the Republic and the Empire, leading Imperial forces into battle and defending the Empire's conquests against Republic counterattacks with fearless determination.[1] In 3660 BBY,[13] Darth Marr drove back a Republic offensive against Korriban, and he dealt the enemy another grievous defeat when the Republic attempted to strike atZiost.[1] By the end of the war, Marr had trained an apprentice of his own in Darth Lachris, who was a fierce warrior at heart who understood the bitter necessity of politics like her master.[7] He also took an interest in certain Force-sensitive individuals within the Empire, such as the brother of Talos Drellik, and would often personally take them to the Sith Academy on Korriban.[14] Marr was known throughout the Republic as the masked Dark Councilor who had defeated entire armies and halted dozens of Republic assaults,[1] and he was one of only seven members of the Dark Council who was still alive by the time[15] the Treaty of Coruscant ended the war in 3653 BBY.[10]

Over the next decade—a time that became known as the Cold War—Darth Marr devoted himself to preparing the Empire for the next conflict, strengthening Imperial defenses and exerting control over his Sphere of Influence to ensure that the Republic would find no cracks in the armor of the Empire. After MoffXerxian failed to quell an uprising on the Imperial-conquered world of Sullust, the man was summoned to a private audience with Darth Marr. After the meeting, Xerxian dictated a letter of resignation and shot himself, leading to many rumors about what had happened. The most predominant one was that the Sith Lord had removed his mask and allowed Xerxian to view his supposedly ruined face.[1]

Darth Marr and Darth Mekhis were two Dark Councilors who survived the war

When the prototype Imperial warship Voidstar was rediscovered, Marr ordered an Imperial strike team to reclaim the vessel before the Republic could capture the derelict dreadnaught.[16] Governor Lysennius Melchiro's[17] continued failure to suppress the Balmorran resistance on the conquered planet Balmorra eventually led to his removal by the Dark Council, and Marr's former apprentice Darth Lachris was selected to take Melchiro's place.[18] After a Republic assault on the world failed, Lachris' forces captured a large number of Republic troopers and several Jedi, and the Sith Lord delivered the captive Jedi to Darth Marr so that the Dark Councilor could attempt to break the prisoners and convert them to the dark side of the Force.[19]

Not long afterwards, Darth Marr and the other Councilors were summoned to Korriban by fellow Dark Councilor Darth Baras. Darths Hadra and Acharon were forced to attend via hologram with Decimus, as the two had joined Decimus in overseeing the Imperial offensive on Corellia. At the meeting, Baras attempted to declare himself Voice of the Emperor—the individual through whom the Emperor delivered his commands—and therefore take control of the entire Empire, but Baras was interrupted by the arrival of Darth Vowrawn and Baras' former apprentice. The Sith Warrior had been appointed as the Emperor's Wrath, and Marr reprimanded Darth Ravage when his fellow Councilor agreed to Baras' request that the Council kill his former student. Declaring the Wrath's challenge was valid and supported by Vowrawn, one of the Council's own members, Marr pitted Baras and his student against each other: whichever was victorious would be acknowledged by the Council as a true servant of the Emperor. As Marr and the other Councilors watched from their seats, the Wrath battled the false Voice in a duel within the Council chamber. But as Baras began to falter, he appealed to Darth Marr to defend the Emperor's Voice, but Marr refused. Ravage did the same when Baras ordered him to attack, and a defiant Baras continued to rage at the Council and the Wrath until his former student executed him. Marr then led the rest of the Dark Council in acknowledging the Wrath's position and right to free reign, but hinted that the Council would not take kindly to actions that contradicted their own designs before the Wrath departed.[5]

After Baras' body was removed from the chamber, Darth Thanaton—recently ascended to the Council after the suspicious death of his predecessor Darth Arctis—rose to address his fellow Dark Lords. He appealed to the other Dark Councilors to aid him in destroying his rival and subordinate Lord Kallig, whom Thanaton had recently declared a Kaggath upon. The Kaggath, an ancient Sith ritual duel, had ended on Corellia when Thanaton had fled to Korriban to meet with the Council, and Thanaton was angered to see that Kallig had followed him to Korriban when the young Sith Inquisitor entered the chamber. Darth Mortis and Ravage mocked Thanaton's reliance on ancient tradition, and Marr cut short the Councilor's speech by bringing up the matter at hand: why was Thanaton, a Dark Councilor, unable to kill a single Sith Lord? Furious, Thanaton began to duel Kallig, and their battle ended when the young Sith forced Thanaton to his knees in submission.

Darths Vowrawn, Marr, Mortis, and Ravage observe the fallen Thanaton

As the drained Dark Councilor struggled to rise, Marr rose from his seat to join Ravage, Vowrawn, and Mortis in front of their fallen fellow, and they watched as Mortis broke Thanaton's neck to put him out of his misery. When Ravage expressed his disdain for Thanaton, Marr reprimanded his fellow Councilor, stating that Thanaton had been a better Sith than Ravage gave him credit for. The Councilors then offered Kallig with Thanaton's now empty seat; Ravage protested as they can't put just a Lord on the Council, but Marr silenced him as Kallig had earned the right. Marr named the young Inquisitor "Darth Nox" and bestowed the new Dark Councilor the Sphere of Ancient Knowledge. [22]

After the deaths of Decimus, Hadra, and Acharon and the Republic victory at Corellia,[23] Marr ordered GeneralHesker and all Imperial forces to retreat from the planet and redirect to the new battlefield of Ilum.[24] Mortis, Ravage, and Marr also dispatched Grand MoffIlyan Regus to Ilum.[25] Around this time, the Dark Council met to discuss the successor to Hadra's seat on the council. Marr, who was full aware of the Empire's declining situation, nominated Darth Karrid, and urged the other Councilors for their support since the Empire's soldiers and resources were dwindling. To his dismay, the other Councilors present supported Darth Gravus, mainly due the Empire's discrimination against non-humans. When Karrid killed Gravus, Marr was surprised by the Council's sudden decision change of support for Karrid, but also concluded that these recent actions were just another example of Sith infighting.

In 3639 BBY Marr gained word of the Hutt Cartel's activities on the planet of Makeb and contacted the Empire's heroes to handle the threat. Upon meeting each of them individually, he explained that he had chosen them to deal with it because he had the rest of the war on his hands since the Emperor was still absent. With the Republic growing closer to victory, the Hutts had seized Makeb to mine isotope-5, a substance capable of twisting gravitational and electromagnetic fields, making it a potent power source, which the Empire desperately needed for their defenses. Marr assigned a limited support team to assist the heroes, but warned them to proceed with stealth and avoid anything that could expose their intentions to the Hutts and the Republic.

Unfortunately, Marr was later displeased to learn that the Hutts had used all the available isotope-5 to create war droids and that their over-mining of Makeb's core threatened to tear the planet apart and the isotope with it. After stressing that three Imperial worlds had fallen to buy the Makeb team time, the latter managed to stabilize the planet's core and keep it secret from their enemies. After hearing of the success of the Empire's activities, Marr redesignated his whole focus onto the galactic war.

Soon after, the Empire had located the defected Dread Masters' base of operations on Oricon. Knowing that any plans of the now-rogue Masters were no good for everyone in the galaxy, Marr contacted the Empire's heroes once again and told them to look for Lord Hargrev, who was supposed to have responded to Imperial comms. He told the heroes that the Dread Masters must be stopped or everything will be lost.

The activities of the Nova Bladespirates working for the Order of Revan remapped the hyperspace lines, luring Darth Marr fleet to Rishi as the same time as the Republic forces under Satele Shan. The two fleets engaged each other, but were interrupted when an associate of Lana Beniko revealed that the battle was orchestrated by the Revanite traitors aboard both fleets. Upon learning that Revan was still alive, Marr agreed for a temporary truce to Republic forces under the command of Grand Master and met with Satele Shan in the town of Raider's Cove on Rishi's surface. Marr revealed to both the Republic and Imperial forces that he became aware of the Emperor's plan to extinguish all life in the galaxy and that he had no wish to serve as a pawn for the Emperor's insanity. Marr explained that if Revan were to revive the Emperor as he planned to, everyone else would be unable to stop him from carrying out his plan to eradicate all life in the galaxy and that Revan had to be stopped from bringing the Emperor back from his incorporeal form. The combined fleets joined forces and traveled to Yavin 4, where they established a coalition in order to spot Revan.

Darth Marr with Satele Shan, Lana Beniko and Theron Shan on Yavin 4

Upon setting up a base camp on the surface of Yavin 4, it became clear that Republic and Imperial rank and file still did not trust each other and had to be convinced to stand against Revan together. Both Marr and Shan sensed a strong presence in the Force on the moon, which was neither the reborn Revan, nor the Emperor. After two sides established sensors enabling them to scout the area near the Temple of Sacrifice, they picked up a signal which Marr recognized as belonging to the Imperial Guard training facility. Marr and Beniko detained commandant Iven amidst the Revanites that ransacked the facility, after which Marr questioned him to discover more details about the Emperor and Revan's plans for him. The combined forces of Republic and the Empire cleared the way to the Temple of Sacrifice, after which the most powerful members of the Coalition went to confront Revan directly. In the final battle against Revan, Marr fought alongside Satele and Theron Shan, Lana Beniko, Shae Vizla and the WookieeJakarro for the future of all life the galaxy. After a difficult fight and despite being temporarily overpowered by Revan throughout the fight, the group managed to defeat him. Despite their efforts, the Emperor returned to life, feeding on the deaths the Coalition caused among the Revanites, which greatly puzzled Marr, as the Emperor did not take a physical form or possess a body and left Yavin 4 as soon as he appeared. Revan finally became one with the Force and in the aftermath of the fight Marr appointed Lana Beniko as the leader of the new Sith Intelligence. Darth Marr then rechristened the Emperor's Wrath as the new Wrath of the Empire and places Darth Nox among the Elite of the Dark Council then proceed to tell them that they were the only Sith Lords he could trust.

Soon after the events on Ziost, Darth Marr led a Republic and Imperial joint fleet into Wild Space in search of both Vitiate and the unidentified invaders who had raided several planets of the two major galactic powers before then retreating back into unknown space. The fleet was composed of seven vessels, including Marr's own destroyer as flagship. Marr sensed he was getting closer to Vitiate and knew if he found him, he would get the Dark Council to send more forces although he doubted the Republic would contribute further, despite their useful assistance until then. Suddenly, the Eternal Fleet appeared in front of the Republic and Imperial forces and engaged them, shooting several boarding pods into the flagship. Skytroopers, the enemy boarders, caused chaos across the entire ship as Darth Marr helped to protect the bridge. Despite his efforts in trying to prevent the ship's loss, he eventually determined that there wasn't anything more he, or his companion, the Outlander, could do and asked the latter what to do next.

After the loss of his ship and the respective battle, Marr and the Outlander were held captive aboard PrinceArcann's ship and taken to the Eternal Empire's capital of Zakuul. There, the prince brought them to his father, the empire's leader, EmperorValkorion, who Darth Marr quickly understood to be just another identity of Vitiate. Marr and the Outlander revealed their purpose being there was to destroy Valkorion but the latter offered that they join him instead. Darth Marr bluntly refused Valkorion's offer and proceeded to attack and defeat several of the Emperor's guards. Before Darth Marr could continue further, he received a direct hit of concentrated lighting from Valkorion's hand, killing the Sith Lord.[26]

Though his physical body had died, Marr, unwilling to leave the Sith Empire undefended, became a Force ghost. Five years later, his spirit communed with Satele Shan as they sensed the presence of Valkorion. Later, they both traveled to Odessen, the home base of the Outlander's Alliance, comprised of elements from both Empire and Republic, united against the Eternal Empire. Though Satele admired their commitment, Marr lamented that many would die in the war to come.[27]

Marr and Satele later happened upon the Outlander after the latter had received a portion of Valkorion's power, rendered unconscious as a result. The pair debated whether to spare or execute the Outlander, but ultimately decided on the former, seeing that the Outlander represented the last vestige of hope in the galaxy. Marr remained invisible as Satele interacted with the Outlander, eventually revealing himself as Satele described Arcann and the Knights of Zakuul's views on the Force. Marr told the Outlander that to defeat Arcann, they needed to gain new perspectives and new weapons. As the Outlander collected a series of items throughout the valley, Marr counseled that defeating Arcann was not enough and said that the Outlander was destined to take the Eternal Throne to restore order to the galaxy, claiming that any other path would lead to chaos.

After facing a vision of Vaylin in a dark cave, Marr cautioned that it was a warning from the Force that Arcann and Vaylin had an army at their command to face any who would oppose them. He then instructed the Outlander that their previous weapon was built for a different war and time and they would need to construct a new weapon that would unite the galaxy and ultimately defeat Arcann. After the weapon was constructed, Marr predicted that the Outlander would defeat Arcann in their next confrontation, but cautioned that leading the Alliance was far different than their previous role.

After the Outlander finished their final trial at the jurgoran's oasis, Marr told the Outlander that the Alliance would collapse if the Outlander did not know who they were inside and the ideal they serve. Having given all they had to impart, Marr and Satele sensed a calling in the Force indicating that their exile on Odessen was over, and departed.[28]

Darth Marr was a human male who was famous for never revealing his true face—the Dark Lord was perpetually encased in his personalized suit of battle armor, and rumor had it that the sight of Marr's visage was the reason Moff Xerxian committed suicide. Throughout his tenure on the Dark Council, Darth Marr's body slowly transformed as a result of immersion in the dark side of the Force, and by the time war broke out again with the Republic the Sith Lord was aware that his body would not last much longer.[1] Marr was driven by a fierce dedication to warfare, one that bordered on zealotry. He believed that conflict was the only way that life evolved and grew stronger, and Marr's personal view was that death was inevitable—only cowards tried to avoid that which was a necessity. Darth Marr's power in the dark side gradually stripped him of emotion over the decades, leaving the man with a fraction of his humanity but a strong desire to ensure that the Empire survived.[1]

The Sith Lord understood that the Empire needed to evolve in order to survive, and he was frustrated by his fellow Councilors' bigotry and the way that they clung to the old anti-alien philosophies even after the Empire began opening its ranks to alien species following the defeat of the traitorous Darth Malgus at the Battle of Ilum.[4] In addition, Marr was different from most Sith who viewed the Jedi with contempt. Instead he respected them as warriors and Force Wielders, even viewing Jedi Grand Master Satele Shan as the only one in the galaxy worthy of being his equal. Marr was also aware that the continuing of backstabbing and infighting would destroy the Empire and tried to keep it under control in the Emperor's absence. Marr was disappointed when Karrid chose to destroy Gravus for her own ends, which made her a Dark Councilor, but made the Empire more vulnerable.

Marr developed a great deal of respect for Thanaton, telling Ravage that he was a better Sith than Ravage gave him credit for, and also telling Darth Nox that he had never thought to see the day Thanaton would fall.

Following his death, Marr acknowledged that his unbendable resolve made him brittle and developed a new interpretation of the Force, acknowledging the truth in the final mantra of the Jedi code, "There is no death, there is only the Force", and it has a plan.

A Sith Warrior, Darth Marr was a remarkably powerful practitioner of the dark side; his strength was such that he ascended to a seat on the Dark Council while still in his early twenties,[1][9] and he was able to maintain his position over the next forty years while the tenure of some Councilors lasted mere weeks. He wielded a single red-bladed lightsaber in combat while protected by his specialized suit of Sith battle armor, and his prowess in battle was such that he had a reputation for routing entire armies.[1] Darth Marr was also skilled in using Force lightning, as he was able to summon a crackling storm of lightning at a moment's notice in order to threaten the impudent Teneb Kel.[12]

In post-class story content for The Old Republic, Darth Marr becomes a major NPC, assuming a leadership role in the Empire and acting as the immediate superior and quest-giver for Imperial players (a role filled by Satele Shan and Leontyne Saresh for the Republic).